The invention relates to the interconnection and packaging of electronic components and, more particularly, to a circuit module which may include a sensor and be disposed in a harsh environment.
As used herein, the term xe2x80x9ccircuit modulexe2x80x9d refers to an interconnection substrate such as a printed circuit board (PCB) having electronic components mounted thereto. A PCB is a multi-layer substrate, having alternate layers of insulating material and conductive material. The conductive material of a conductive layer is patterned to have conductive xe2x80x9clinesxe2x80x9d or xe2x80x9ctracesxe2x80x9d for routing signals (and power) from one location on the PCB to another location on the PCB. In the case of multiple conductive layers, typically at least one of these layers is disposed on a surface (e.g., the xe2x80x9ctopxe2x80x9d surface) of the PCB. Additionally, the conductive layer on the top surface of the PCB may be patterned to have xe2x80x9cpadsxe2x80x9d which serve as terminals for (i) connecting to leads of electronic components mounted to the PCB, or (ii) making connections to external instrumentalities such as sockets. In this manner, electronic components which are mounted to the PCB may be interconnected to one another via pads on the top surface of the PCB and conductive traces of the PCB.
Examples of electronic components which may be incorporated in a circuit module include:
(a) xe2x80x9cactivexe2x80x9d electronic components such as integrated circuit (IC) devices, and the like;
(b) xe2x80x9cpassivexe2x80x9d electronic components such as resistors, capacitors, and inductors (including transformers), and the like;
(c) switches, relays and the like; and
(d) sensors, transducers and the like.
The electronic components incorporated in a circuit module may either be xe2x80x9cpackagedxe2x80x9d or xe2x80x9cbarexe2x80x9d (not packaged).
An example of a xe2x80x9cpackaged electronic componentxe2x80x9d is a semiconductor memory device (e.g., dynamic random access memory, or DRAM, chip) which has been mounted and electrically connected to a leadframe having a plurality of elongate conductive members (xe2x80x9cfingersxe2x80x9d) and overmolded with plastic. Outer portions of the leadframe fingers extend (protrude) out of the molded plastic body and can be connected to the conductive pads on an interconnection substrate (PCB). In this manner, a plurality of plastic-packaged DRAM memory devices can be mounted and connected to a PCB, thereby forming a memory module. The memory module can be plugged into a socket which is mounted on another interconnection substrate, such as a xe2x80x9cmotherboardxe2x80x9d of a computer system, with conductive pads disposed on one or both surfaces of the memory module making electrical contact with resilient contact members in the socket.
An example of a xe2x80x9cbare electronic componentxe2x80x9d is a semiconductor device which is glued (using xe2x80x9cdie attachxe2x80x9d adhesive) onto an interconnection substrate and electrically connected thereto with fine wires extending between pads on the semiconductor device and pads on the interconnection substrate. In order to protect the electronic component and the wires, it is known to apply a dollop of xe2x80x9cglob-topxe2x80x9d epoxy, or the like, over the electronic component and the fine wires.
A well-known technique for making such connections to semiconductor devices is xe2x80x9cwirebondingxe2x80x9d. An exemplary wirebonding technique involves:
a. feeding a fine (e.g., 1 mil diameter) gold (or gold alloy) bond wire through a capillary which is located above a terminal (pad) of an interconnection substrate or electronic component mounted thereto;
b. bonding (e.g., welding) an end of the bond wire to the terminal using a combination of pressure and heat or ultrasonic vibration;
c. withdrawing the capillary so that the bond wire xe2x80x9cpays outxe2x80x9d of the capillary, thereby forming some slack in the bond wire;
d. moving the interconnection substrate (or, conversely, the capillary), so that the capillary is located above another terminal (pad) on the electronic component or interconnection substrate;
e. bonding an intermediate portion of the bond wire to the other terminal; and
f. severing the bond wire, thereby resulting in a xe2x80x9cloopxe2x80x9d of bond wire extending between the terminal (pad) on the electronic component and the terminal (pad) on the interconnection substrate.
The present invention draws upon many of the techniques described hereinabove to effect a novel technique for packaging electronic circuit modules and components. Prior to proceeding with a description of the invention, certain additional relevant aspects of electronic packaging should be understood.
There is often a need to test or, more broadly, exercise electronic components and circuit modules prior to their being shipped for installation (e.g., assembly into systems) to ensure that they will perform to their design specification. This would include, in the case of electronic components and circuit modules that can and need to be calibrated or personalized, calibrating or personalizing the electronic components and circuit modules.
Returning to the example of a DRAM device which has been overmolded with plastic and which has outer portions of leadframe fingers protruding out of the molded plastic body, the DRAM device can be tested by making xe2x80x9ctemporaryxe2x80x9d electrical connections to portions of the leadframe fingers which protrude from the package body, using pins, needles and the like. An example of a pin suitable for making a temporary electrical connection to a terminal (in this example, the terminal being the protruding portion of the leadframe finger) of an electronic component is a so-called xe2x80x9cpogoxe2x80x9d pin, which is generally a pin having an inner part protruding from an outer part, and a spring maintaining the inner part biased to an extended position. Or, in the case of a memory module having a plurality of plastic-packaged DRAM memory devices mounted and connected to a PCB, the entire module can be tested by plugging the module into a test socket of a test system, the test socket making temporary electrical connections to the PCB and xe2x80x9caccessingxe2x80x9d the components mounted to the PCB via the conductive traces of the PCB.
Personalizing or calibrating a packaged circuit module similarly involves, in a broad sense, having access to protruding terminals of the module. For example, the module may have a non-volatile memory (NVM) component which can be programmed by providing signals to external terminals of the module. Or, for example, a module can be programmed via personalization components such as DIP-switches which are part of the module and accessible from external the module.
In contrast thereto, consider the case of a packaged circuit module which in its final form does not have any terminals protruding from its exterior or access to personalization components from its exteriorxe2x80x94not even power connections (e.g., battery terminals). The problem is, how to exercise the module. An example of such a packaged circuit module lacking the inherent ability of be exercised or personalized in its final form is a transponder module that is fully encased to isolate its electronic components from the ambient environment, save for a sensor (e.g., a temperature sensor) that is exposed to the ambient environment on the exterior of the packaged circuit module.
As will become evident, the present invention is directed to a package for encapsulating electronic modules and components having at least two chambers (cavities).
European Patent No. EP-A-0289439 discloses a single chamber of an enclosure which is partially filled over a first circuit module, thereby encapsulating a xe2x80x9cfirst chamber,xe2x80x9d and leaving the unfilled remainder of the chamber as a xe2x80x9csecond chamber.xe2x80x9d A second circuit module is placed on top of the first filling, and then the second chamber is filled with a second filling which covers the second circuit module. Appropriate interconnections between circuit modules and external connectors are made by conductors embedded in the first and second fillings, and thereby passing between chambers.
U.S. Pat. No. 5,239,126 (Sony, 1993) discloses a high-frequency circuit package including a conductive substrate, and upper and lower shielding cases which define upper and lower shielding chambers, respectively. High-frequency circuits are mounted on the upper and lower surfaces of the conductive substrate within the upper and lower chambers, respectively. This patent, incorporated in its entirety by reference herein, is cited as an example of an electronic package having two chambers.
A similar package with three shielded chambers is seen in U.S. Pat. No. 5,504,659 which discloses a structure for she shielding of electronic components from outside electromagnetic fields. The outside housing holds a single printed circuit board which separates a xe2x80x9cpollutedxe2x80x9d space from a xe2x80x9ccleanxe2x80x9d space and accommodates the components of the device to be shielded itself. In FIG. 2, the polluted space (24) forms one chamber, and the housing forms a shielding partition which divides off a clean space (28) forming a second chamber with through contacts for lines connecting between the chambers. The printed circuit board also serves to shield the first two chambers from a third clean space (32) on the other side of the printed circuit board in the housing.
U.S. Pat. No. 5,627,406 (Pace, 1997), incorporated in its entirety by reference herein, discloses an electronic packaging module. A hybrid circuit (310) forms a base and has protuberances (330) and metallic pads (331) on its surface. Semiconductor devices (340) and other components (341) are bonded to the protuberances and pads. A metal or ceramic frame (350) having openings for the semiconductor devices and other components is disposed on the surface of the base and fits around the semiconductor devices and other components. Plugs (370) fit inside the openings in the frame, contact the back of the semiconductor devices, and are bonded to the frame to seal the module. Although this packaging module is not an encapsulation module, it is referenced as illustrative of a package having two (or more) side-by-side cavities (or chambers) with electronic components disposed in each of the cavities.
In some cases, a circuit module is intended to be disposed in a xe2x80x9charshxe2x80x9d environment, and it is desirable to isolate the electronic components of the circuit module from the environment. An example of such an application for a circuit module is an RF transponder which is disposed within a pneumatic tire of a vehicle. Attention is directed, for example, to the PNEUMATIC TIRE HAVING INTEGRATED CIRCUIT TRANSPONDER AND PRESSURE TRANSDUCER described in commonly-owned U.S. Pat. No. 5,218,861, incorporated in its entirety by reference herein.
It is an object of the present invention to provide an improved electronic module and method for packaging the improved electronic module as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary objects.
It is therefore an object of the present invention to provide an improved technique for packaging electronic circuit modules.
It is another object of the present invention to provide an improved electronic module package.
It is another object of the present invention to provide a technique for packaging an electronic circuit module which permits the electronic module to be encapsulated (potted), then exercised (e.g., calibrated), then separately potting additional electronic components disposed within the package.
According to the invention, a package for encapsulating electronic components has at least two chambers (cavities). The chambers are open at their tops so that the chambers, and electronic components and modules disposed within the chambers, can be at least partially filled with encapsulating material (potting compound). The chambers are suitably molded from a plastic material such as thermoset epoxy, polyphenylene sulfide, Ryton TM, or the like, by an injection molding process.
According to an aspect of the invention, a leadframe is disposed within the package and has elongate conductive elements (leadframe fingers) extending from a one of the chambers into an other of the chambers. In this manner, an electronic component or module disposed within a one of the chambers can be interconnected with an electronic module or component disposed within an other of the chambers.
According to an aspect of the invention, the chambers may separately (individually) be filled with encapsulating material. This permits, for example, an electronic module disposed within a one of the chambers and connected to portions of leadframe fingers within that cavity to be potted with encapsulating material, then electrically exercised (e.g., calibrated or personalized) by making temporary electrical connections (e.g., with xe2x80x9cpogo pinsxe2x80x9d) from an external instrumentality (e.g., a test apparatus) to portions of the leadframe fingers extending into an other of the chambers. The potted module within the one of the chambers can thus be exercised, either with or without an electronic component disposed in the other of the chambers. After exercising the potted module, the other chamber and electronic component disposed therein can be potted without xe2x80x9cdisturbingxe2x80x9d the previously-exercised, previously-potted module.
In an embodiment of the invention, an outer one of two chambers surrounds an inner one of two chambers. This embodiment includes having a one chamber surrounding an other chamber which, in turn, surrounds yet another chamber.
In another embodiment of the invention, a one chamber is adjacent another chamber. This includes having more than one chamber adjacent another chamber, such as two chambers on opposite sides of an other chamber, or three chambers adjacent the sides of a triangular chamber, or four chambers adjacent the sides of a rectangular chamber.
According to an aspect of the invention, the sidewalls of a one of the chambers may be higher than the sidewalls of an other of the chambers. In this manner, the chamber having the higher sidewalls can, for example, be fully filled with encapsuling material while minimizing a risk of the encapsulating material spilling over into a neighboring chamber.
According to an aspect of the invention, a portion of the leadframe may extend through an outer wall of the package to the exterior of the package.
According to another aspect of the invention, openings may be provided in an external surface (outer wall) of the package for making connections with components which are external to the package.
In a representative application for the package, the electronic module and components contained (and potted) within the package comprise an RF-transponder and a pressure sensor, and the entire package assembly may be mounted within a pneumatic tire.
Other objects, features and advantages of the invention will become apparent from the description that follows.